SEM_GETVALUE(3) |
FreeBSD Library Functions Manual |
SEM_GETVALUE(3) |
NAME
sem_getvalue —
get the value of a semaphore
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include < semaphore.h>
int
sem_getvalue( sem_t * restrict sem, int * restrict sval);
DESCRIPTION
The
sem_getvalue() function sets the variable pointed to by
sval to the current value of the semaphore pointed to by
sem, as of the time that the call to
sem_getvalue() is actually run.
RETURN VALUES
The
sem_getvalue() function returns the value 0 if successful; otherwise the value -1 is returned and the global variable
errno is set to indicate the error.
ERRORS
The
sem_getvalue() function will fail if:
-
[
EINVAL]
-
The
sem argument points to an invalid semaphore.
STANDARDS
The
sem_getvalue() function conforms to ISO/IEC 9945-1:1996 (“POSIX.1”).
The value of the semaphore is never negative, even if there are threads blocked on the semaphore. POSIX is somewhat ambiguous in its wording with regard to what the value of the semaphore should be if there are blocked waiting threads, but this behavior is conformant, given the wording of the specification.